To The Stars And Back
by bookiealchemist
Summary: Natsu is Lucy's celestial spirit. A spirit hard to befriend, reluctant to talk to her, but always ready to fight for her well-being. [Celestial Spirit/Celestial Mage AU]


_**To The Stars and Back**_

* * *

Lucy knew the key was special the moment she landed her eyes on it.

A perfectly silver key, with a flame on its design, warm to the touch of her hand. She could feel the power emanating from it, despite being a simple silver.

The magic store where she got it was special too. Dark, but powerful as well. With the sad man behind the counter, dressed in black and white and a heartbreaking look, it shouted not to be normal.

"That key is special," the young man said. "Its power will bring you trouble. You better forget all about it."

The warning did scare her the tiniest bit, but Lucy was determined to become a celestial mage as powerful as her mother Layla, and for it she'd need all the help she could get. She only had three golden keys so far, but her journey would definitely allow her to get more.

"I still want it," Lucy said, grabbing the bloody red box where the key laid inside. She placed it before the man, who now glared at her with hate. Doing her best not to squirm under the hatred, she continued. "How much is it?"

"50.000 jewels." the man said.

Lucy choked on her own saliva.

* * *

She returned to her little new apartment right after exiting the scary magic store, anxious to meet her new friend.

She closed the door and placed her bag over the couch, before taking a quick glance at the keys in her possession. Three golden and now 6 silver's. She smiled sweetly at all of them, she loved her spirits.

Even if Aquarius hated her, Lucy would love her first friend until the very end.

Taurus and Cancer always helped her in rough times. And fashion crisis times.

Crux, Horologium, Lyra, Plue (Nikora), and Pyxis were always there for her too.

She wondered how this new friend would affect her life. The man at the shop told her its name was E.N.D., not cheerful at all, but she still wanted to make friends with the spirit. For her, they were her friends. She didn't want to be a celestial mage to use them as soulless weapons for wars.

Lucy careful took the key in her hands and eyed it, the delicate pattern giving off warm waves of strength, a little flame adorning it. It did not look evil at all, but that didn't stop her from watching out for any danger.

She held the key in front of her, and gathering her magic in her hand she said, "Gate of the flame demon, I open thee! E.N.D!"

Before her a shining light appeared, and after blinking a couple of times, her vision adjusted in time to see what she not expected.

It was a boy, but it wasn't a the same time. The anatomy of his body resembled the one of a human; one of a very strong young man with a sculpted body. Of course, with the exception of a red, scaly tail that swung from left to right. His skin was almost entirely covered in dark red scales. His hair was weirdly light pink, with black horns coming out from his head. Thankfully, those weren't too big.

He wore baggy white pants and a black and orange vest, weird, but probably fitting for a fight. His feet were bare.

Lucy's gaze stopped when she met his never-ending onyx eyes. Emotionless and deep, with no wish to show her any piece of his thoughts and soul.

Lucy forced herself to snap out of her trance and smile brightly at him.

"Hello, E.N.D.! My name is Lucy and-"

"I don't care." he harshly cut her off, his voice rough and deep, his eyes hard like stone.

Lucy blinked in surprise, that was the first time a stellar spirit showed reluctance to work with her, besides Aquarius, but even she was nice the time they met.

Lucy licked her lips, her mind thinking faster than ever to come up with something. Fool was she to think she was prepared for anything.

"Umm, what?" she sputtered, cursing as she stumbled over her own words, lost under his fierce gaze.

"I'm not interested in working with you," he said. "You can just leave my key alone or throw it to the river, I don't care."

Lucy gaped, a million feelings dwelling in her chest, before she exploded. "Excuse me? What way of talking is that? Why would I want to give up on you? I already consider you my friend! A friend wouldn't throw his friend to the freaking river!"

The look he gave her made her relax. He stared at her blankly, but his eyes were a bit wider, and his mouth was barely open. It taught her he had emotions after all. There was a way of reaching him, and she definitely would do it.

"That's why," she continued, her voice barely above a whisper. She intertwined her fingers under her chest, and maybe or maybe not her cheeks flushed a light pink. "I'd like to be your friend."

It took a him a few seconds to recover his composure. He frowned and crossed his arms over his hard chest, giving her a downgrading look.

"I'll come whenever I want to, not when you call me."

With that being stated, he dissolved into a red light, going back to the Celestial World and leaving her alone in the now empty apartment.

Nonetheless, a shy smile threatened in her lips.

* * *

He was there too, when she joined Fairy Tail.

The guild of love and family and friendship, and the most powerful out there. The guild of her dreams.

He was tired of hearing her complain about how she was not powerful enough to join, or about her insecurities and rambles. He was not her hairdresser to be there to listen to her problems. He was there to fight, because who couldn't love a strength contest?

So one day, he had enough.

After kicking the ass of a group of robbers in the outskirts of Magnolia, E.N.D turned around in the dark alley, the euphoria of victory still in his chest. It was a pretty easy mission that a random lady gave Lucy, but the girl still managed to trip and bruise her leg.

She was sitting against the wall, putting a band-aid over the wound. Her lips were pouting.

Curious, he walked closer to her, his hands inside the pockets of his pants. But with his sharp ear, he could hear her annoyed mumbles from afar.

"If I get hurt so easily, I can't join Fairy Tail," she said, "I'm so clumsy. They'll never get me in."

He rolled his eyes. Another one of her tantrums. Annoying.

He sat over a big box that was by her side, so he could keep an eye over her from above. The bruise wasn't bad at all, just a cut of the size of a finger and as thin as a needle. Her legs were covered on dirt.

She was pathetic.

When she finished taking care of it, she looked up at him, clearly annoyed.

"What? Are you going to make fun of me like always?" she spat. It seemed she was more upset than normal.

"Your pathetic self is not worth my time." he shrugged.

She shot him a glare that was meant to tell him to shut up, but he saw the little tears gathering up in the corner of her brown eyes.

He leaned against the old brick wall, closing his eyes.

"If you want to join that guild so desperately," he added, "Why don't you just do it?"

"It's not that easy." Lucy said, hugging her knees against her chest. "I need to become stronger."

"I can't deny that," he said. "But if that guild is so familiar, they couldn't turn you down, right? What kind of family leaves someone out?"

When she didn't answer, he opened one of his eyes to take a look at her.

She was speechless.

Great. It was hard to leave her out of words. That was something he learned on those five months of being with her.

He stood up and jumped down to stand by her side. She arched her eyebrows questioningly, but instead of explaining, he grabbed her wrist and forced her to keep up with his fast walking.

"W-What are you doing?" she squealed, but he couldn't see how her eyes were fixed in the point where his scaly red fingers grabbed her soft pale skin.

"We're going to the damn guild." he simply said. "I'm tired of hearing you whine."

Her face reddened incredibly as she sputtered, "I-I don't whine! And you can go back to your world if it annoys you!"

"Shut up." he cut her off.

Neither of them spoke until they were standing in front of the large building. Laughter and shouts echoed, sending nervous shivers through Lucy's spine. She was not ready for this. They would surely kick her off as soon as they felt her poor magic-

"What are you doing?" E.N.D. interrupted her thoughts yet again.

"I'm not ready-"

"Shut up." he said, and pushed her inside.

As soon as she stepped in, everyone turned their heads to take a look, but to her surprise, their faces were kind and happy. She turned around to yell at her spirit for doing it, but he had already vanished.

She cursed innerly as she stood awkwardly there, until a kind woman of white hair and radiant smile greeted her.

* * *

That day, Lucy returned as the happiest girl ever to her apartment.

In a short amount of time, she'd managed to join Fairy Tail, get new amazing friends, make herself a new home and get a loving family like the one she always dreamed of.

"Gate of the flame demon, I open thee! E.N.D!"

The demon, or celestial spirit, appeared before her with his eyebrows scrunched together in frustration.

But Lucy didn't care.

Surprising both of them, she jumped into him, hugging him with both her arms around his torso, burying her face in his warm chest.

"W-What's wrong with you!" E.N.D shouted, and in his confusion, he pushed her away.

But Lucy wasn't mad.

Instead, she smiled brighter than ever as she held her right hand in front of his face, showing off her new pink guild mark.

"E.N.D.! Check it out! I've got the mark of Fairy Tail now!"

He watched her flushed face and her smile and how happiness radiated off her.

He turned around, "Ah,"

" _Thank you_!"

* * *

It took her less than a year to be picked to make the S-class mage exam.

And he couldn't help but feel proud.

Even if he didn't want to.

Again he was the first one to hear the news from her the moment she returned home. It didn't surprise him in the very least, after watching her grow endlessly after she joined Fairy Tail. After all, she'd went into every single adventure she could.

He'd learned about her tragic past with her father, and immediately after he stopped making fun of her weakness. She was kidnapped and tortured, but the way she beared with it all made him somewhat develop respect towards her. It was nice her guildmates cared for her enough to try save her, but he ended up being the one catching her falling from a tower and freeing her from the grip of an iron dragon slayer.

He thanked the Celestial Spirit King from teaching him how to pass the gate without her help.

He watched her gain more golden keys from jobs and save his friend Loke. The way she did her best to rescue him was admirable, even if he'd never admit it aloud.

" _It's not a sin! Caring for your friends' feelings is not a sin! If you disappear, then Aries, myself, and everyone here will be filled with sadness! You won't be repenting your sin that way!",_ she'd said.

" _Spirits aren't shields! I fight alongside them! That's my style!"_ she'd assured, and she'd fulfilled.

" _But they feel pain! They have feelings! And yet you call yourself a Celestial Spirit Mage?"_ she'd accused.

She'd dragged him into so many adventures.

He could sincerely say he didn't hate her anymore.

"E.N.D.!" Lucy stormed inside her bedroom. "I'm pairing up with Cana for the exam!"

He arched his eyebrows at her, "Cana? Why? Isn't that bastard of the ice mage stronger than her?"

"Gray is already S-class, so he can't help me," Lucy explained, sitting in her bed. "And Cana!"

Her eyes teared up, scaring him a bit. He straightened his back in his seat, watching her carefully, waiting for her explanation.

"You wouldn't imagine!" she started, "She told me her father is Gildarts, and she's known it all along, but she thinks she is not powerful enough to tell him, because y'know, Gildarts is like the S mage of the S-class mages, and… and," her voice broke at the end. It took her some deep breaths to continue. "Since she failed the exam five years, Master didn't let her took it again, so she says she wants to help me to do it. She says if we succeed and she really helped me, she'd tell Gildarts straight away!

She eyes him, waiting for a reaction.

He shrugged. "Interesting."

"You're heartless!" she moaned, but both of them knew she wasn't serious.

She got up from her seat and went to the kitchen. "I'm gonna make dinner. Are you staying or…"

"I'm going." E.N.D. said.

"Okay!"

He still didn't understand why she always was so willingly to cook dinner for him. Eating wasn't essential for the celestial spirits, but enjoying a meal still felt good. Besides, Lucy's cooking was delicious. Specially her homemade chocolate cookies.

He stared at the wall opposite him for a while, thinking, until he asked,

"Why are you always so worried for your friends?"

Lucy's head popped out from the kitchen. She frowned in confusion, her nose covered in white cream.

"Because you're all my friends, obviously."

* * *

He didn't understand what was going on.

The S-Class Mage Promotion Trial was under enemy attack.

From what Lucy told him, a dark guild called Grimoire Heart came in and started to attack all of Fairy Tail members. Most of them were hurt, others still fought for their pride as the number one guild.

And suddenly Lucy was by his side yet again, a fierce and determined look in her doll face. Her body was covered in scratches and her clothes were ripped apart, barely covering anything.

They were facing a rather odd enemy, fat and purely white, with only a loincloth covering him. Despite his appearance, he was strong and gave Lucy a hard time until he arrived.

"So, what's the plan?" He asked, eyeing his partner.

He didn't remember when he started calling her that, but it felt righteous.

Not that he'd say it loud, anyways.

"His magic is weird," she said, frowning at their opponent. "He uses a doll with your hair and then your body mimics the actions."

"Then don't let him get your hair," he simply stated. She was really weird sometimes.

She pursed her lips in thought. "I wish it was that easy… That guy is really strong."

"Then I'll attack while you think," he said, running into battle.

"Wait!" she shouted, but it was too late.

The white man threw a fist against him, which he easily blocked, but the strength was too much and it sent him flying backwards until his back hit a mountain of rocks. He fell to the ground, but when he was about to get up, rocks fell over his legs.

He fought to get up, but Lucy was tired and she didn't have that much power at the moment, so he didn't have enough power to move the rocks.

"E.N.D.!" Lucy shouted and ran to him, but Kain Hikaru hit her with his arm, and her body flew to the ground.

The monster kneeled beside her body, obviously not hearing his desperate shouts, and he grabbed her head.

They were close enough for him to see the struggle and pain in her face. And it killed him.

"Lucy!" he shouted. Her eyes opened a little. "Run away! Leave me alone! I'll figure out how to get off here!"

"No way!" Lucy screamed back.

And in that moment Kain decided to crush her against the hard floor again. And again. And again.

"Lucy!" he squeaked, desperate. The situation was only getting worse and worse and it was his duty to take care of his summoner.

"There's no way I'm running away," Lucy said, and between all the dark and pain of the moment, she managed a smile that took his breath away.

But it was wrong. So wrong.

 _That_ was forbidden between humans and celestial spirits.

"Lucy, you need to go away!" he repeated.

No.

 _No._

And with that smile, she said, "No! Running away by myself? No way. It's always more fun when we are together!"

His eyes widened with shock at her words, and his heart did something so weird inside him. Did spirits even have a heart?

But he ignored it, because love between humans and celestial spirits was forbidden by the most ancient laws of the world and who was he to go against it?

His eyes caught glimpse of the doll by his side. If what Lucy told him was correct, it still had the hair of Kain, and he could just save her. Ignoring her screams of pain, he did his best to reach the doll.

He caught it and cracked its arm, and instantly Kain's shouts of pain echoed on his ears.

He did it.

He saved Lucy.

Even if wasn't enough to defeat him, he saved her for the moment and that was more than enough. He'd think of a plan later.

Because in that moment, he didn't know the fear of facing a powerful dragon, or how heartbreaking Lucy's scared face could be, or how he'd hold her hand in her last moments.

For seven years, he'd be in the celestial world waiting for her return.

Seven years of uncertain mourn.

Seven years fighting against love.

* * *

He didn't show any signs of emotions when she returned.

Lucy didn't what to think as all of her other spirits hugged her and he stayed in the corner of the room, watching them all.

His face was blank and hard when she tried to hug him too, because it didn't matter what he felt during those seven years, she missed him so much it physically hurt.

It kinda hurt when he refused her embrace -like a needle stabbing her heart a bunch of times until the point she wanted to cry and scream into her pillow.

But the back of her mind thought it was for the best.

Maybe he, too, sensed that flickering flame of something else inside her every time he stepped into her vision, and he wanted to prevent it to igniting stronger.

Because she knew it too.

The ancient law that forbid all bond between humans and spirits that went deeper than friendship.

And despite acting so cold towards her, E.N.D. was the one to lend her a hand and a shoulder to cry when she learned her father died a week before her return.

* * *

Both of them knew there was no going out of the situation.

Neither of them knew when did things go downhill so fast.

First, the Magic Council blew up like a fireworks show, leaving only one survivor. Then Laxus and the rest got badly injured. Third, the guild blew up too, yet again. A lot of fights went on, they invaded the dark guild, Tartaros, base. They only found demons.

Everything was so dark.

And then, Alegria was set off and all of her guildmates disappeared.

Lucy felt alone, being the only one left. Where were her friends? She didn't want to be alone in this dark, scary cube.

Her loneliness didn't last long.

Suddenly the demon called Jackal appeared before her, his thirst for blood obvious in his face. Preferably her blood.

She summoned Virgo, a great spirit friend of hers, but Jackal was too strong. She thought E.N.D had put an end to him back in that village, but it seemed it wasn't like that.

She ran and ran, her tired legs moving as far away as she could of the demon. And suddenly the corridor was filled with water, and another strong-looking demon appeared. She summoned her other friend Loke, who tried his best, but failed as well.

Another demon appeared, looking like a girl with an angry face. The aura coming off her wasn't as strong as the others, but she still could give problems.

Lucy didn't have enough magic to summon anymore.

She tried to defend herself with her whip Fleuve d'étoiles, but Jackal's explosions burned in her skin and made her fall. With watery eyes, she wistessned the demon kill his comrade, the demon girl, cold-hearted. It filled her heart with anger.

Virgo was still fighting with the water demon, and Loke tried to block Jackal's way.

She was running out of options.

Lucy took a deep breath and touched all of her keys. She had two options.

Her mind told her one thing, but her heart said otherwise.

Cursing to herself, she took her favorite silver key out of the belt and summoned him, before collapsing.

But before she touched the ground, strong, warm arms wrapped around her and held her close. She was home.

"What the heck are you doing, Lucy?" E.N.D screamed, his eyes full of worry as he stared at her hurt body.

She managed a smile, "You came."

"Of course I'd come!" he screamed hysterically. She'd never seen him like this. "How… how did you open three gates simultaneously?"

Lucy barely shrugged.

"You're too strong, Lucy." He said. "Close Loke's and Virgo's."

She obliged, apologizing to the spirits when they stared at her shocked before going back to their world.

E.N.D. hugged her tighter and closer.

"Lucy, I can't defeat those demons, you know?"

She nodded.

"Then why did you call me?" he asked. "We're in water, maybe Aquarius could have done something-"

"I wanted to see you." she cut him off.

"L-Lucy?" he asked. She could only picture in him a flustered face, despite being so difficult all the time they'd known each other. She wanted to see his blush.

Lucy leaned in his chest. Jackal was staring weirdly at them, probably thinking she had something planned.

Eternal seconds passed before he spoke again, this time, his voice much more serious.

"Lucy. There is a way to rescue your friends."

It took all in her to look up to his face. His gaze was determined, and for some reason, fear went up her spine. His plans always left something.

"It is told that if a celestial mage can open three doors at the same time, he can open the gate of the Celestial Spirit King and summon him."

"What?"

"But to do it," he continued. "You need to break a powerful key. Normally it'd be a gold one, but let's say long ago I did something and that Old Man owes me. If you destroy my key, I'm sure he'll come."

"Wait what-"

"You don't have other option, Lucy. Hurry up."

Lucy's mind became a fuzz as she watched him, trying to look all heroic and stuff while breaking her heart and soul into million pieces.

"I… I don't want to lose you!" she stated, blinking back threatening tears.

"There's no other way!" he insisted. "Do you want to lose a gold key?"

"Of course not!" Lucy replied, her voice at the edge of breaking down. "They're all precious friends of mine."

"Then hurry up!"

"But… But if I lose you…"

"Lucy…"

"I'd be so lonely, stupid!" she shouted, tears finally streaming down her face.

E.N.D. stared at her, shocked by her reaction.

It was the first time ever that someone cried for him.

For the mere mention of losing him.

And Lucy's sobs broke him.

But he knew that it was the correct thing to do. Lucy had to save those fairies from the demons' fangs.

He bit back the words that wanted to spill out of his mouth, for their sakes.

"You know," he added, his voice much quieter and softer than it'd ever been. "My name is Natsu."

Lucy looked at him through tears, so hurt and broken. "Then, _Natsu_ , don't leave my side. Please. I beg you."

His name had never sounded that good.

Taking a deep breath, Natsu took her hands in his and squeezed them. "C'mon, Lucy. Break my key. I can't hold that bastard off much longer."

Lucy shook her head. "You can't ask me to do that!" she cried.

Feeling brave, Natsu leaned in and touched her forehead with his. She did her best to keep eye contact, but she was just crying so much it hurt.

"Lucy," he said. "Break my key. I promise you we'll see each other again."

"You promise?"

"I promise."

He let her go.

She took a deep breath and tried to calm her sobs as her shaking arm lifted up the silver key. It shocked him to know how much she trusted his words.

It was nice to have someone trust you, even if you only were saying lies.

Because maybe he wouldn't die, but not seeing her ever again felt like death itself.

It was weird. She was weird.

He remembered hating her when they met and months after that, but somewhere along the road, the little crying brat had grown up and made him fall.

"Open…" she said, her voice creaky, "Gate of the Spirit King!"

The key started to shine, and Natsu knew he had bare seconds.

Lucy turned around to give him a last glance. "I love you, Natsu."

He smiled sadly at her, "I love you too, Lucy."

The key broke.

And he disappeared forever.

* * *

 _Dear Natsu,_

 _It's been nineteen years since we last saw each other._

 _But I still hold onto your promise. I want to see you again. I miss you so much._

 _I don't think I've thanked you enough for sticking with me, even though you hated me at first. After all, you were the one that encouraged me to go to Fairy Tail. How can I even thank you enough for that?_

 _In some way or another, you changed my life. I can't lie. I don't want to._

 _I still have your broken key here with me. I use it around my neck every day, all the time. I don't care what others think or say. I just want to see you._

 _How are you doing? I know I ask this every week when I send you a letter, but you never reply. I still believe you will one day. I want to know how you're doing, I'll always care about you._

 _Loke told me you're just sitting alone there. Don't be. You need to make new friends and go on new adventures, without me. I know it's difficult to move on. It took me two years._

 _But I am fine now. I have friends and a family that support me. My new book got published the other day. It's like a dream, even if you used to say I'd suck as a professional author._

 _That's it, for now. Nothing much happened this week._

 _Thank you again for saving all of us so many years ago. Fairy Tail will always remember your bravery._

 _Thank you for saving me. Thank you for being always by my side._

 _I still love you, as weird as it sounds. I'll always love you, to the stars and back._

 _Get better,_

 _Lucy._

* * *

 _ **Word Count= 4665. Ahhh I hope you liked this one-shot I wrote for New Year (even if it's late XD). This is based on a post I saw on Tumblr that said Mashima's original idea was to make Natsu a celestial spirit. I hope I did it fine.**_

 _ **I'd love to hear what you have to say about this! Thank you so much for reading!**_


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